<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>字符串大小写转换</title>
</head>
<body>
<script>
function toUpperCase(str){
    return str.toUpperCase();
}
function toLowerCase(str){
    return str.toLowerCase();
}
var yuanzifuchuan = "www.jb51.ITCASE.CN";
alert("原字符串为：" + yuanzifuchuan);
alert(toUpperCase(yuanzifuchuan));
alert(toLowerCase(yuanzifuchuan));
</script>
</body>
</html>